The present invention relates to a new and improved rolling cover means for covering a guideway for a sliding carriage or slide of a machine tool.
In its more particular aspects, the rolling cover means of the present development is of the type comprising two rolling bands, meaning windable and unwindable bands, each of which is affixed to the sliding carriage with one of its ends and extends away from the sliding carriage along the guideway in one respective direction. The guideway has two opposed ends, and there are provided two drums, each of which is disposed at the region of a respective one of the ends of the guideway, each of the drums being rotatably journaled for rotation about an axis extending transversely relative to a longitudinal direction of the guideway and being structured to wind-up and wind-off a respective one of the rolling bands. There are also provided two wheels, each of which is connected to a respective one of the drums to provide torque transfer or transmission. Moreover a tension member extends around both of the wheels and can be rolled-off upon the wheels free of slip.
Prior art rolling cover means as described, for example, in German patent publication No. 2,946,825, published May 21, 1981, in particular as depicted in FIGS. 1 and 4 thereof, each having both of the drums journaled for rotation upon a respective shaft which, in turn, is journaled for rotation at the guideway. Each shaft is connected to the associated drum by means of a torque-transferring helical or coil spring extending around the shaft within the drum. Each of the shafts has an end projecting from the associated drum where there is mounted a gear. A toothed belt extends around the gears of both of the shafts and both ends of the toothed belt are secured to the sliding carriage. When the sliding carriage or slide moves along the guideway both the gears and the coil springs of both the drums are driven by means of the toothed belt in such a way that the rolling band is wound-up upon the drum at that side towards which the sliding carriage moves, while the other rolling band is unwound from the associated drum. The coil springs arranged within the drums balance the respective increase and decrease in the roll diameter occurring during winding and unwinding of the rolling bands. Also, the coil springs hold the rolling bands under tension.
In this known arrangement as discussed hereinbefore, the spring excursions are smaller than with other prior art rolling cover means, wherein the springs connect the associated drum to a stationary component, and thus, there must be performed spring excursions which are proportional to the entire path of travel of the associated rolling band. However, even in the prior art structure described in greater detail hereinbefore, the spring excursions at any rate, are not so small as to be negligible in the event that the associated rolling band has such a long wind-up length that the rolling band is multipley wound-up around the associated drum. The larger the spring excursions required for winding and unwinding the rolling band, that much smaller is the specific load which is permitted at the spring during continuous operation. In the case of rolling cover means provided at guideways for rapidly reciprocating sliding carriages, however, the rolling bands must be tensioned by using considerable forces in view of their mass inertia, in order to provide for a sufficiently rapid wind-up operation. The required tensioning loads will further increase in case that the rolling bands are enclosed at both sides over their width by wiping seals and in case that the lateral edges thereof are guided between sealing ledges, as is particularly required for hydrostatic carriage guideways. Consequently, it cannot be avoided, then, with the prior art rolling cover means as described hereinbefore, that, in case of specifically high loads, the torque-transferring springs arranged within the drums will have to perform more or less long spring excursions. When such a spring breaks during a rapid movement of the sliding carriage, then it is hardly unavoidable that the rolling band which is pushed by the sliding carriage buckles, thus becoming unusable, possibly even destroying the associated sealing ledges. Furthermore, in the disclosed prior art arrangement additional space is required for the connection between the sliding carriage and the toothed belt in accordance with FIG. 4 of the aforementioned German Patent Publication No. 2,946,825.